interrupts: Fix context switching to U-mode from S-mode

This ensures that kernel code never gets skipped or otherwise messed with. The first switch to U-mode is handled explicitly elsewhere by manually calling process.switchTo on the init process.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/interrupts.zig b/src/interrupts.zig
index ba5f440..9d47934 100644
--- a/src/interrupts.zig
+++ b/src/interrupts.zig
@@ -130,11 +130,13 @@ export fn handleTrap(epc: usize, tval: usize, cause_bits: usize, hart_id: usize,
                     // before returning into it.
 
                     process.list.last.?.data.pc = epc;
+
+                    schedule() catch |err| {
+                        std.debug.panic("Hart {d}: Unable to schedule next process: {any}", .{ hart_id, err });
+                    };
                 }
 
-                schedule() catch |err| {
-                    std.debug.panic("Hart {d}: Unable to schedule next process: {any}", .{ hart_id, err });
-                };
+                // Don't interrupt kernel code, it may never run otherwise.
             },
             .supervisor_external => {
                 const context: u14 = @intCast(2 * hart_id + 1);